1. Field of the Invention
The present invention relates to a method and an apparatus for display characterization, and more particularly, to display characteristic characterization method and apparatus, which rewrite a display device's profile by reflecting color calibration variable values of a display set by a user in display device's profile.
2. Description of the Related Art
Even if a computer system sends identical control signals (specifying the same combination of electron beam intensities) to different displays, many variables, including differences between various brands of graphics cards and CRT display hardware, variations in the circuitry controlling each of the beams of a display, the age of the phosphor dots on which the beams are incident, the ambient lighting conditions around the display, and the strength of the Earth's magnetic field, will affect the actual color perceived by a user. Thus, it is preferable to measure and calibrate at least two characteristics of a display: “gamma” and “white point”.
“Gamma” denotes the relationship between the input digital value (or voltage) sent from a computer system's graphic card and imaging application software to a display and the light intensity emitted from the display. Many variables, including the age and composition of phosphor, the type of graphics cards, the type of display, and ambient lighting condition, will affect this relationship. The “white point” of the displays is the display's color when a computer causes maximum values of red, green and blue light to be emitted from the display.
Electronic devices generally use a kind of file such as a profile, in order to characterize their color reproduction capabilities. The profiles are like a data dictionary recording color data such as the gamut of the electronic device, the characteristics of phosphor or colorant used to generate colors, the brightness and chromaticities of the white point, and the operational mode of the electronic device and are generated in a device characterization process during manufacture of the electronic device.
The color characterization of a color display is performed by measuring output colors (generally corresponding to chromaticity and brightness) with respect to input values (generally corresponding to RGB values) of the display and identifying the relationship between the output colors and the input values. The color characteristics of the display, is stored as a color profile and is used to perform color matching. Accordingly, in order to write a color profile through the color characterization of a display, an expensive color measuring apparatus is necessary.
In some cases, display manufacturers provide with a display device's profile which can be applied only to a single fixed color characteristic state. In other words, the display device's profile can be used only in one particular set of color characteristic conditions, set by the display manufacturers. However, these color characteristic conditions set by the display manufacturer, do not satisfy users' demands to freely change the color characteristics of the display, and need to be changed when the viewing environment changes. Since most displays include means for calibrating colors and their brightness, it is possible to control brightness, contrast, and color temperature which relates to the characteristics of displayed white. When color characteristic conditions previously set by the display manufacturer are changed by a user, the display device's profile does not reflect the changes, and thus color matching between an input device and an output device cannot be carried out correctly.
In the prior art, there is a method for measuring color characteristic variables using a characterization tool having a color sensor, used on a display when color characteristic conditions set by the display manufacturer are changed by a user. However, in the case of using such a color sensor, additional expenses are necessary, and must install the characterization tool in the display control system, such as a computer, and run the characterization tool himself.
In order to solve the above problems, a method for characterizing a color display by visual measurement has been disclosed in U.S. Pat. No. 5,381,349. In this method, a transfer function concerning the brightness characteristics of a display is determined by finding a point at which the brightness of a calibration color patch, comprised of the brightest pixels interposed with the darkest pixels at a certain ratio, matches the brightness of a comparison color patch, and repeating this process using calibration color patches with different ratios of the brightest pixels to the darkest pixels. With this method, the brightness characteristics of the display device can be obtained without using an additional color measuring apparatus; however, the user must repeatedly carry out experiments, and the accuracy of the transfer function obtained from the experiments may vary according to the user. In addition, since this method can give the user only the brightness characteristics of a display, it is impossible to reflect the color temperature characteristics of the device in the display device's profile.
U.S. Pat. No. 6,075,888 discloses a technique of writing a new profile by reflecting new color characteristics of a display in an old profile. In this method, an original profile can be corrected and used. This method uses a color measuring apparatus in order to obtain data required to correct a profile. However, in this method, a user must perform color measurement, and expensive equipment is required.